Extract the pixel values of a pixel image at each point along a linear transect.

```
transect.im(X, ..., from="bottomleft", to="topright",
nsample=512, click=FALSE, add=FALSE, curve=NULL)
```

An object of class `"fv"`

which can be plotted.

- X
A pixel image (object of class

`"im"`

).- ...
Ignored.

- from,to
Optional. Start point and end point of the transect. Pairs of \((x,y)\) coordinates in a format acceptable to

`xy.coords`

, or keywords`"bottom"`

,`"left"`

,`"top"`

,`"right"`

,`"bottomleft"`

etc.- nsample
Integer. Number of sample locations along the transect.

- click
Optional. Logical value. If

`TRUE`

, the linear transect is determined interactively by the user, who clicks two points on the current plot.- add
Logical. If

`click=TRUE`

, this argument determines whether to perform interactive tasks on the current plot (`add=TRUE`

) or to start by plotting`X`

(`add=FALSE`

).- curve
Optional. A specification of a curved transect. See the section on Curved Transect.

If `curve`

is given, then the transect will be a curve.
The argument `curve`

should be a list with the following
arguments:

- f
A function in the R language with one argument

`t`

.- tlim
A numeric vector of length 2 giving the range of values of the argument

`t`

.- tdescrip
(Optional) a character string giving a short description of the function argument

`t`

; defaults to`"curve parameter"`

.

tname(Optional) a character string giving the symbolic name
of the function argument `t`

; defaults to `"t"`

.

The function `f`

must return a 2-column matrix or data frame
specifying the spatial coordinates `(x,y)`

of locations along the
curve, determined by the values of the input argument `t`

.

Adrian Baddeley Adrian.Baddeley@curtin.edu.au and Rolf Turner r.turner@auckland.ac.nz

The pixel values of the image `X`

along a line segment
will be extracted. The result is a function table (`"fv"`

object)
which can be plotted directly.

If `click=TRUE`

, then the user is prompted to click two points on
the plot of `X`

. These endpoints define the transect.

Otherwise, the transect is defined by the endpoints
`from`

and `to`

. The default is a diagonal transect from
bottom left to top right of the frame.

`im`

```
Z <- bei.extra$elev
plot(transect.im(Z))
```

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